A one-dimensional hologram represents a line image, so it may be regarded as a special aspect of a two-dimensional hologram. And, equally, it may be deemed as a generalized or a multiplexed expansion of a diffraction lattice. A certain one-dimensional hologram is identical to a common diffraction lattice with a constant lattice period and constant periodic strength. That one-dimensional hologram is formed by interference of two parallel rays of proper incident angles. The two-dimensional image is obtained by sequential scanning of the line images those are expressed by one-dimensional holograms. Therefore, it is naturally appropriate for displaying motion pictures.
There are few studies on the one-dimensional hologram in the past. However, its possibility may be expected by considering the dimension of the information of displaying a picture. It is possible to prove the presence of the one-dimension hologram with calculation. The one-dimensional hologram may be a new useful device for allowing people to see a plane picture. The one-dimensional hologram is more advantageous under certain circumstances as compared to the conventional device.
As one example of the above-described circumstances, there is a HMD (Head Mount Display) application. Because it is a new device, the one-dimensional hologram would be applied to various fields that we have never expected. Here, the one-dimensional hologram will be compared with the conventional art in the field of a HMD type portable display device. In the conventional art, there are a technology of using a common plate display device, a method of deflecting a parallel ray for thereby forming a certain picture, and a conventional hologram method. In the case of using a plate display device, the current motion picture HMD display devices operate in this method. There are currently many applications, but there are many limitations in their image qualities and conveniences.
In a method of deflecting a parallel ray, Fujitsu et al developed a method of forming a diffraction lattice pattern with variable pitches, but it is not practical yet. In this method, there are problems in high resolution displaying due to a limit of displaying speed and a high-order diffraction problem.
In addition, a common two-dimensional hologram method may be deemed as an ultimate method, but it needs very large amount of computational load when computing the hologram data. Too large amount of data is needed to express a common hologram, and it is difficult to manufacture an optical modulator capable of expressing a hologram pattern, for that reason, it is difficult to put to practical use.